Merge pull request rancher#3015 from dweomer/update-readme-v1.5.6

readme: update for v1.5.6

Bump up user docker 19.03.11

Bump up user docker 19.03.11

Add networking info for collect_rancheros_info.sh

Roll back kernel 4.14.138-rancher

Bump rancher/os-hypervvmtools and rancher/os-openvmtools

Support for flushing cert to initrd only

Adjust log output

Bump rancher/os-hypervvmtools to v4.14.138-rancher-1

Add a script that can flush custom certs to iso file